Fiber optic networks are commonly used to transfer large amounts of digital voice, video, and/or data throughout communication networks. These fiber optic networks transfer data through a series of fiber optic nodes. Fiber optic connections typically support a significantly higher data transfer rate than is necessary to transmit the data of any single network user, under-utilizing significant amounts of bandwidth. In order to better utilize this tremendous bandwidth potential, multiple streams of data from multiple network sources are frequently combined into a single data stream and transmitted over a single fiber optic cable. The electronic equipment necessary to achieve this multiplexing comes at a significant cost. One way of combining multiple streams of data is a technique known as Wavelength Division Multiplexing (WDM). WDM transmits different streams of data over a single fiber optic cable by simultaneously transmitting the different streams of data at different wavelengths of light. Upon receipt of a WDM signal, the different wavelengths of light are separated, and the original data streams are reconstituted. By utilizing WDM techniques, some Dense Wavelength Division Multiplexing (DWDM) fiber optic nodes can simultaneously transmit 32 or more channels of data, each channel having a capacity of 10 gigabits per second, for instance.
In addition to WDM techniques, it is possible to multiplex many streams of data into a single fiber optic data stream using Time Division Multiple Access (TDMA) multiplexing (or “time division multiplexing”). Time division multiplexing cycles through multiple source data streams, transmitting a segment of each source data stream over a time slice of the multiplexed data stream. Upon receiving the multiplexed stream, time division de-multiplexing is applied to break the stream into its component source data streams. One key to efficient Time Division Multiplexing is the availability of accurate synchronization information. Unlike packet-switched networks, OSI Layer 1 protocols used in fiber optic transmissions contain no internal indication of the beginning or the end of a time slice, and so identification of the beginning and the end of a time slice requires accurate synchronization. When available, external timing sources typically provide this synchronization information. Current methods of distributing synchronization to different nodes in the fiber optic network for use in WDM multiplexing include transmitting synchronization information over a traffic-bearing channel, and installing a reference timing source in proximity to each node in the network. There is a need for reliable yet low-cost means of distributing synchronization information to nodes in a WDM fiber optic network without consuming a traffic-bearing channel, and without the expense of installing a primary reference timing source in proximity to every node in the network.
The description below addresses these and other shortcomings in the present art.